A frequency modulation is generally used to send signals comprising a succession of symbols, each symbol being associated with a frequency, in order to then read them by detecting the frequency. It has been proposed to use phase-locked loops to detect the frequencies used. However, such a solution can work only for signals with a signal-to-noise ratio of good quality.
It is also possible to apply a fast Fourier transform processing operation, well known to a person skilled in the art by the acronym “FFT”, to retrieve the symbols contained in the signals.
Applying a fast Fourier transform processing operation has the drawback of requiring a large number of samples that correspond to as many frequencies to be processed to be obtained previously in order to read the symbols. Since the complexity of the calculation increases by O(n.log(n)) (big O notation, or Landau notation), n being the number of samples, the need to use a large number of samples makes the processing of a message by fast Fourier transform particularly complex.
Although such an FFT-based solution is suitable for processing signals that have been sent in a very noisy environment, this solution has the drawback of being too complex. “Very noisy” should be understood to mean an environment in which the signal-to-noise ratio in reception is of the order of −10 dB to −20 dB.